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battle of the cape cod! insulating and venting upstairs, moisture problem

battle of the cape cod! insulating and venting upstairs, moisture problem

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  #1  
Old 02-03-14, 06:35 AM
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battle of the cape cod! insulating and venting upstairs, moisture problem

i bought this cape 4 years ago, upstairs there is 2 bedrooms, it was originally insulated ceiling/roof rafters with balsam wool insulation 2 gable vents at the both peak ends no venting down low, new roof with full length ridge vent. needless to say it was cold up stairs..

in one bedroom i remodeled, i removed all the old insulation i then insulated the knee walls with r15 and between the ceiling joists with roxul r23, r30 in the flat center ceiling part, with soffit vent baffles running from the crawl space up to the ridge. there is no vapor barrier on the roxul

i noticed the other day only on the north side of the house the bottom of the roof deck is wet, and moisture dripping from the baffle vents.. top of roxul is wet where it's pressed against the baffle vents.

currently this is how it's vented.

one gable vent other side of house has been blocked.

ridge vent at peak

4 soffit vents on front and back of house each side 16" wide

baffle vents that run from the crawl space to the ridge (not all the way down to the soffit)

i think i should add some more venting.

also i've been using a small humidifier, holds 4 gallons of water that i've been running non stop for a few months, it's on the first floor central on the north side, it has a built in automatic fan and humidistat set for 50% would this contribute to moisture in the attic only on the north side?
 
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  #2  
Old 02-03-14, 11:03 AM
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Yes, turn the humidifier off. North side is the cold side so it is probably not the location of the humidifier that is creating the moisture in that area, but the cold.

Moisture moves through most materials, but moisture problems are most often related to air leaks. Warm humid air leaking into a cold poorly vented space is a recipient for disaster. Even 25% indoor humidity would be bad.

If the footprint of your house is 1,200 ft², then you need a total of (about) 8 ft² of net free vent area (NFA), half low and half up high, and distributed evenly. I'll let you calculate what you have.

The real trick is going to be locating and sealing any air leaks. Plumbing, electrical, and chimneys are frequently major sources.

Did you do any air sealing during this renovation?

Bud
 
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Old 02-03-14, 01:11 PM
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when i did the single upstairs bedroom there was really nothing to seal, they have tongue and grove panels on top of the floor joist that extend in the crawl space, i did turn off the humidifier.

i'll have to calculate the venting, i know for a fact what i have now is not enough and block off the gable vent.

i have the sealed recessed lights in the ceilings with r30 over them in one bedroom not the other where i have moisture in the north side.
 
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Old 02-03-14, 01:27 PM
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Battle of the cape cod

We are assuming there is a complete ceiling and wall covering (drywall) in theses rooms, correct?

The air barrier Bud talks about is critically. If you have a ceiling and wall finish with a number of holes in it you are feeding moisture laden air to the rafter or wall bays. This leakage path can be problematic but that is not to say that moisture (vapor) working through the materials does not also make a contribution to the total load. A vapor "barrier" on insulation is not really a barrier, the flow of moisture is slowed but it still is occurring 24/7..

Definitely in agreement about killing the humidifier for awhile. If you have been having the same weather I am in PA you should be in the 20% range, a range you will unlikely be able to achieve.

Most people in the building industry never think about it but the styrene foam vents that you are using for ventilation are good at creating an air channel for keeping an air flow between the roof deck and the vent but moisture coming through the ceiling assembly will not readily pass through the vent, thus with cold air traveling up the channel any moisture below it can condense on the bottom side of the vent.

Again, as Bud stated, the north will typically exhibit the worst issues as the roof deck is not subjected to any solar gain. A deck of osb or plywood would more readily show condensation as opposed to solid lumber sheathing but under the right circumstances solid wood can even show condensation.

As far as adding more ventilation, it does not always PREVENT condensation but it does aid in drying it out.
 
  #5  
Old 02-03-14, 03:32 PM
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Where does your bath fan vent, outside away from the soffit vents?

We know you have excess moisture and it is not coming from the outside, very dry air out there. So it has to be from the inside. The humidifier is probably the reason you noticed a problem and the symptoms may disappear as the RH drops, but you will still want to pursue other leaks over time. I'll add a link to Efficiency Vermont's air sealing guide.

I'll also add a link on vapor diffusion retarders to better understand moisture control. The building science corp link will also lead to tone of related reading.

BSD-106: Understanding Vapor Barriers — Building Science Information

http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud

Oh, and don't worry about the gable vents, they are fine being left operational. They will actually increase the air flow from the soffits.
 
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Old 02-03-14, 05:28 PM
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thanks for the replies, what you said about the styrene foam vents is exactly what i'm seeing, moisture on them.

the bathroom fan when i bought the house just blew up in the crawl space, i attached a insulate ducting pipe right to the outside of the house via a dryer vent, not at the soffit. i'm good there.

the one room with that i redid is completely covered with drywall, now this brings up a good question....

the other room i was working in, it had a dresser built-in in one of the knee walls on the north side, i had ripped that all out, it was open for a few days but this was months ago, i insulated the whole area but no sheet rock was installed yet.

my house is 32' wide the finished room being the largest, would leaving that one space open a short while cause moisture at the other end of the house?

good stuff, thanks for the insight/help
 
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Old 02-03-14, 06:26 PM
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Water vapor moves freely throughout a structure and wants to equalize. It does move more readily on air currents but as I said earlier it migrates through building elements on a perpetual basis(diffusion).

Now, to make things even more confusing, under some conditions ventilating air can be your enemy. This happens when you get a sudden warm-up in winter accompanied by perhaps a rainy few days. The relative humidity would be 100% in outdoor air and that air entering the attic space as ventilating air would encounter the sheathing, which....in the initial stages of this episode, would still be cold, perhaps just from a good chilling in the pre warm-spell or perhaps it still has a snow pack on it. When that ventilating air (100%RH) hits that cold sheathing, condensation results. Kind of leaves you in a real quandary as to what to do!!

You haven't said much about the living space on the first level but again, air currents migrating through framing junctions, light fixtures, soffits, pipe holes, wiring holes,etc. all contribute to the free movement of vapor.

The hole relative to the built-in dresser is probably not relevant to the issue you are experiencing currently but as I stated earlier, moisture migrates throughout a structure to equalize vapor pressure so what is happening in the bathroom will typically impact the entire house to some degree given an appropriate time frame to allow movement and equalization.
 
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Old 02-04-14, 02:11 AM
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When you removed the built-in dresser you would have installed some framing for the new drywall. The new bottom plate section might not be continuous with the other bottom plates. A gap or seam there would be a path for warm air under the bottom of the drywall. Air leaks under the bottom plates as well.

The insulation in the cavity below the kneewall needs a solid block to prevent air from circulating between the warm and cold spaces. Fiberglass insulation will not stop air flow. Is the insulation exposed at the floor in this north side attic?

Bud
 
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Old 02-04-14, 06:43 AM
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when you ask if the insulation is exposed, do you mean the back side of the fiberglass to the crawl space? the lower knee wall fiberglass is faced. the back side is currently open to the crawl space as i was not finished, the other finished room is completely covered with tyvek paper on the knee wall portion where it meets the crawl space
 
  #10  
Old 02-04-14, 06:55 AM
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The back of the kneewall should indeed be covered to minimize air flow through the insulation, the tyvek is one option. I was thinking about the floor below the kneewall. Sometimes that floor is missing or doesn't cover all of the insulation all the way to the soffits. This link may help:
Two Ways to Insulate Attic Kneewalls - Fine Homebuilding Article

Bud
 
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Old 02-04-14, 10:13 AM
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thanks Bud, that last link on page 2 "keep the attic outside" is how mine is setup.
 
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Old 02-04-14, 11:35 AM
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Note the solid blocking directly below the kneewall. Very important. Also, the insulation in the floor is completely covered. That diagram includes a rim joist at the ends of the floor/ceiling joists. Some construction omits that and results in some exposed insulation near the soffits.

Where is the moisture forming?
Those soffit vents are open to this space which then flows via the baffles to the upper attic and out either the gable vent/s or the ridge vent. Is that correct.

If that blocking is missing, then any moisture or air leaks into the ceiling below the floor will have access to those cavities. However, if those chutes in each rafter cavity are not blocked, those side attics should be venting reasonably well.

Bud
 
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Old 02-04-14, 04:35 PM
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Bud, i'm going to investigate a little deeper, i know one of the cavities (floor/bottom ceiling joist) had blocking, i'll have to check them all.

i have all those baffles in each joist with roxul r23 after that. the baffles stop in the 2 cavities the lower crawl and upper ceiling.

i can feel the air as i put my hand behind the roxul.

moisture is forming between the roxul insulation and the foam baffles, but it only appears towards the lower half of the angled ceiling closer to the crawl space, the insulation was not wet in the upper portion.

i just looked i may have a few issues, there is a rim joist at the end of the floor joist with a 2x4 on top that the rafters sit on, i noticed there are some boards missing on top where i can see the insulation between the ceiling joists, i just looked at the roxul it's really wet on top and my concerns are growing about the water issue, partly because i feel like i created the issue by venting the area.

i'll keep you posted.
 
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Old 02-04-14, 04:54 PM
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"i can feel the air as i put my hand behind the roxul."
As calvert said, the baffles will be cold. The rule is, no warm air can reach a cold surface. Is there an air seal (block) at the bottom of the Roxul?

I'm still not following your description very well. Do you have baffles down by the soffits or just from the top of the kneewall up into the upper attic. That air path has to allow warm moist air in the side attics to be pushed up and out.

Bud
 
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Old 02-04-14, 05:29 PM
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the air baffles stop just past the top of the knee wall, i did not put blocking at the end of the roxul, there is some missing sub floor in the crawl space where i pushed down on the ceiling insulation and felt all my heat

this attic did not have soffit vents previously and there were no signs of condensation, just the ridge and 2 gable vents at the top.

should i close off the soffits and leave it unvented? this seems to be where the problem started when i let in all the cold air...

it seems i have a lot of air sealing to do, so if my heat/moisture is working up through the ceiling this is what should be causing the moisture on the lower half of the roxul, it's not necessarily the roxul touching the foam vent baffles? i just want to be sure when i seal it up that there will be no hidden condensation. the upper portion of the vents/roxul closer to the top flat ceiling have no sign of moisture.
 

Last edited by zchrisz; 02-04-14 at 05:47 PM.
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